The present disclosure relates to processes for preparing latex emulsions and toners. More specifically, continuous processes for polymerization of a polyester utilizing a polycondensation reaction and continuous processes for emulsification of the polyester are described.
Processes for forming toner compositions for use with electrostatographic, electrophotographic, or xerographic print or copy devices have been previously disclosed. For example, methods of preparing an emulsion aggregation (EA) type toner are known and toners may be formed by aggregating a colorant with a latex polymer formed by batch or semi-continuous emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
As noted above, latex polymers utilized in the formation of EA type toners may be formed by batch or semi-continuous emulsion polymerization. Batch processes for producing resins may be subjected to bulk polycondensation polymerization in a batch reactor at an elevated temperature. The time required for the polycondensation reaction is long due to heat transfer of the bulk material, high viscosity, and limitations on mass transfer. The resulting resin is then cooled, crushed, and milled prior to being dissolved into a solvent. The dissolved resin is then subjected to a phase inversion process where the polyester resin is dispersed in an aqueous phase to prepare polyester latexes. The solvent is then removed from the aqueous phase by a distillation method.
The use of solvents in this process may cause environmental concerns. For example, if the solvent level is not low enough (<50 ppm), extensive waste water treatment and solvent remediation may be required.
In addition, where a batch process is utilized, because the individual batch process involves the handling of bulk amounts of material, each process takes many hours to complete before moving to the next process in the formation of the toner, that is, aggregation and/or coalescence. In addition, batch-to-batch consistency is frequently difficult to achieve because of variations that may arise from one batch to another.
It would be advantageous to provide a process for the preparation of a latex resin suitable for use in a toner product that is more efficient, takes less time, results in a consistent toner product, and is environmentally friendly.